Bald Eagles

The Bald Eagle (Haliaeetus leucocephalus) is a bird of prey found in North America that is most recognizable as the national bird and symbol of the United States of America. This sea eagle has two known sub-species and forms a species pair with the White-tailed Eagle. Its range includes most of Canada and Alaska, all of the contiguous United States and northern Mexico. It is found near large bodies of open water with an abundant food supply and old-growth trees for nesting.

When to see them at USeeWildlife

The bald eagle is usually found on camera 8 from mid-November thru the end of February. Most are migratory, but a few resident eagles visit during the spring and summer. They mostly feed on fish in the lake, but we have seen them catch the occasional duck or turkey as well. Up to seven have been spotted at one time including both juveniles and adults. We see them most often when temperatures dip below freezing, and fish in the lake begin to surface.

Description

The Bald Eagle is a large bird, with a body length of 71–106 cm (28–42 in), a wingspan of 183–234 cm, (72–96 in), and a mass of 3–7 kg (6.6–15.5 lb); females are about 25 percent larger than males. The adult Bald Eagle has a brown body with a white head and tail, and bright yellow irises, taloned feet, and a hooked beak; juveniles are completely brown except for the yellow feet. Males and females are identical in plumage coloration. Its diet consists mainly of fish, but it is an opportunistic feeder. It hunts fish by swooping down and snatching the fish out of the water with its talons. It is sexually mature at four years or five years of age. In the wild, Bald Eagles can live up to thirty years, and often survive longer in captivity. The Bald Eagle builds the largest nest of any North American bird, up to 4 meters (13 ft) deep, 2.5 meters (8 ft) wide, and one tonne (1.1 tons) in weight.

The species was on the brink of extirpation in the continental United States (while flourishing in much of Alaska and Canada) late in the 20th century, but now has a stable population and has been officially removed from the U.S. federal government's list of endangered species. The Bald Eagle was officially reclassified from "Endangered" to "Threatened" on July 12, 1995 by the United States Fish and Wildlife Service. On July 6, 1999, a proposal was initiated "To Remove the Bald Eagle in the Lower 48 States From the List of Endangered and Threatened Wildlife." It was delisted on June 28, 2007.

The plumage of an adult Bald Eagle is evenly brown with a white head and tail. The tail is moderately long and slightly wedge-shaped. Males and females are identical in plumage coloration, however females display sexual dimorphism in that they are 25 percent larger than males. The beak, feet, and irises are bright yellow. The legs are unfeathered, and the toes are short and powerful with large talons. The highly developed talon of the hind toe is used to pierce the vital areas of prey while it is held immobile by the front toes. The beak is large and hooked, with a yellow cere.

The plumage of the immature is brown, speckled with white until the fifth (rarely fourth, very rarely third) year, when it reaches sexual maturity. Immature Bald Eagles are distinguishable from the Golden Eagle in that the former has a more protruding head with a larger bill, straighter edged wings which are held flat (not slightly raised) and with a stiffer wing beat, and feathers which do not completely cover the legs. Also, the immature Bald Eagle has more light feathers in the upper arm area, especially around the very top of the arm.

Body length ranges from 71–106 centimeters (28–42 in). Adult females have a wingspan of up to 2.44 m (96 in), while adult males may be as small as 1.68 m (69 in). Adult females weigh approximately 5.8 kg (12.8 lb), males weigh 4.1 kg (9 lb). The size of the bird varies by location; the smallest specimens are those from Florida, where an adult male may barely exceed 2.3 kg (5 lb) and a wingspan of 1.8 m (6 ft). The largest are Alaskan birds, where large females may exceed 7.5 kg (16.5 lb) and have a wingspan of over 2.4 m (8 ft).

The average lifespan of Bald Eagles in the wild is around 20 years, with the oldest living to be about 30. In captivity, they often live somewhat longer. In one instance, a captive individual in New York lived for nearly 50 years. As with size, the average lifespan of an eagle population appears to be influenced by its location.

Habitat and range

The Bald Eagle prefers habitats near seacoasts, rivers, large lakes, and other large bodies of open water with an abundance of fish. Studies have shown a preference for bodies of water with a circumference greater than 11 km (7 miles), and lakes with an area greater than 10 km² (3.8 square miles) are optimal for breeding bald eagles.

The Bald Eagle requires old-growth and mature stands of coniferous or hardwood trees for perching, roosting, and nesting. Selected trees must have good visibility, an open structure, and proximity to prey, but the height or species of tree is not as important as an abundance of comparatively large trees surrounding the body of water. Forests used for nesting should have a canopy cover of less than 60 percent, and as low as 20 percent, and be in close proximity to water.

The Bald Eagle is extremely sensitive to human activity, and is found most commonly in areas free of human disturbance. It chooses sites more than 1.2 km (0.75 miles) from low-density human disturbance and more than 1.8 km (1.2 miles) from medium- to high-density human disturbance.

Behavior

The Bald Eagle is a powerful flier, and soars on thermal convection currents. It reaches speeds of 56–70 km/h (35–44 miles per hour) when gliding and flapping, and about 48 km/h (30 miles per hour) while carrying fish. It is partially migratory, depending on location. If its territory has access to open water, it remains there year-round, but if the body of water freezes during the winter, making it impossible to obtain food, it migrates to the south or to the coast. The Bald Eagle selects migration routes which take advantage of thermals, updrafts, and food resources. During migration, it may ascend in a thermal and then glide down, or may take ascend in updrafts created by the wind against a cliff or other terrain. Migration generally takes place during the daytime, when thermals are produced by the sun.

Bald Eagles normally squeak and have a shrill cry, punctuated by grunts. They do not make the scream that is found in films; this is usually the call of a Red-tailed Hawk, dubbed into films for dramatic effect.

Diet

The Bald Eagle's diet is opportunistic and varied, but most feed mainly on fish. In the Pacific Northwest, spawning trout and salmon provide most of the Bald Eagles' diet. Locally, eagles may rely largely on carrion, especially in winter, and they will scavenge carcasses up to the size of whales, though it seems that carcasses of ungulates and large fish are preferred. They also may sometimes feed on subsistence scavenged or stolen from campsites and picnics, as well as garbage dumps. Mammalian prey includes rabbits, hares, raccoons, muskrats, beavers, sea otters, and deer fawns. Preferred avian prey includes grebes, alcids, ducks, gulls, coots, egrets and geese. Most live prey are quite a bit smaller than the eagle, but predatory attacks on large birds such as the Great Blue Heron and even swans have been recorded. Reptiles, amphibians and crustaceans (especially crabs) are preyed on when available.

Reproduction

Bald Eagles are sexually mature at four or five years of age. When they are old enough to breed, they often return to the area where they were born. It is thought that Bald Eagles mate for life. However, if one member of a pair dies or disappears, the other will choose a new mate. A pair which has repeatedly failed in breeding attempts may split and look for new mates. Bald Eagle courtship involves elaborate calls and flight displays. The flight includes swoops, chases, and cartwheels, in which they fly high, lock talons, and free fall, separating just before hitting the ground.